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Folding-Wing Glider: Rockets Up ... Glides Down! 



Make] Projects 

hhiiilH ho/ 1 !/ tuMaal/ chare r\icf*f\\tat* 



build, hack, tweak, share, discover,- 



Folding-Wing Glider: Rockets Up 



. Glides Down! 



Written By: Rick Schertle 



TOOLS: 



Drill and drill bits (1) 

High-speed rotary tool (1) 
e.g., Dremel 

Hobby knife (1) 

if you're hand cutting 

Laser cutter (1) 

if you're laser cutting 

Metal filed) 
for deburring 

Needle Nose Pliers (1) 

Razor blade (1) 

Sand paper (1) 
if hand cutting 

Scroll Saw or Coping Saw (1) 

Tin snips (1) 

if you use a soda can 

Wire cutters (1) 



PARTS: 



Rocket Glider kit (1) 

product #mkrs2 from makershed.com 

Balsa wood sheets (1) 

for the wings and the fuselage, 
respectively 

Hardboard or acrylic sheet (1) 

for the wing pivot. This is a very small 
piece about 1"x 1 A>". 

Wood dowels (1) 

Stiff wired) 

/ used lightweight 18-gauge floral stem 
wire. A straightened large paper clip is 
the right gauge but might be a bit too 
short. 

Plastic tubing (1) 

I used part #226 from 
http://evergreenscalemodels.com: you 
can get creative with something similar. 

Aluminum sheet (1) 

Get it from a hobby store, or cut apart a 
soda can. 

Penny coin (1) 
PlastiDip (1) 

Rubber bands (1) 

for the wing pivot and the catapult, 
respectively 

Staples (2) 



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Page 1 of 1 6 



Folding-Wing Glider: Rockets Up ... Glides Down! 

Glued) 



• Glued) 

such as Gorilla Glue - 1 now recommend 
super glue or CA wood glue (bonds 
ins tan fly and does not expand) 

Fine sand paper (for smoothing out 
balsa, if cutting by hand) (1) 



SUMMARY 

As a kid, I remember my dad talking about this seemingly magical balsa wood rocket glider. 
With the wings folded back, the glider shot into the air using a hand held rubber band 
attached to a stick catapult. Wind resistance held the wings back, then when the glider 
reached its peak, the wings popped open for a long and graceful glide down. Especially 
exciting to me, was when the glider began to wear out, he would attach a fire cracker to it 
and then launch it into a shower of balsa wood confetti glory. 

About ten years ago I began thinking about this glider and whether or not it was still 
available. I found a science supply company who sold one for about ten bucks that looked 
similar so I bought three or four. Wow, these little gems proved to be super fun. I was used 
to the standard hand-toss glider that flew 20 or 30 feet for a few seconds. This one zipped 
straight into the sky to about 60 or 70 feet! Fishing them out of trees and weeds, we played 
with these like kids for hours. Eventually they wore out, but in a recent cleaning out of my 
basement, I came across one mostly intact. This got me thinking about the rocket glider 
again. 

I began researching on the internet about the glider and there was very little information to 
be found. But what I did find, proved quite valuable. For one, the glider I was familiar with 
was no longer being made and had been out of production for some time. This glider was 
based on the original folding wing glider designed by Jim Walker and his company American 
Junior Aircraft Company, in the late 1930's. The patent had long since expired so another 
company made a glider based on the original design. I began communicating with Scott 
Giffith who is the current historian for the Jim Walker's collection. Jim Walker was an 
innovator of a number of products including control line airplanes, a sonic control glider and 
remote control lawnmower. He developed the original folding wing glider called the Folding 
Wing Interceptor in 1939 and after securing the patent, began producing them near Portland 
Oregon. With the development of a tripod style catapult (to be featured in the next issue of 
MAKE) to launch the glider nearly 300 feet in the air, Jim's glider caught the interest of the 

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Folding-Wing Glider: Rockets Up ... Glides Down! 



US Army and the Army began using them for artillery practice during World War II. 232 
million models were produced during the lifetime of the company. In 2004, Frank Macy, 
friend of Jim Walker and long time official historian, made his final reproduction of the 
original Interceptor. Also in 2004, Paul Bradley added some micro remote control units to the 
glider with some success. Paul recently said, "With modern micro R/C a much lighter weight 
model could now be made." 

With these gliders out of production, I had to have a new stock of my own. In the past, balsa 
wood planes would be punched out using a large die machine with metal cutting blades. After 
a certain run, the dies would wear out and need to be replaced. With modern laser cutting 
technology, a perfect cut is achieved every time. Using the one remaining glider I had left, 
with help from some folks at the Tech Shop, I began reverse engineering the project and now 
present it here to MAKE readers as a how-to. Along with MAKE, I've also developed it into a 
handy kit available from the Maker Shed with the parts pre-cut and ready to fly in just about 
an hour. Like many fans of this glider over the years... pull the glider back on the hand-held 
catapult, aim straight up and let it rip! 

Videos of Flight - My Son 

Video of Flight - Me 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 1 — Cut the parts. 



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• If you have the kit, you can skip this step and any other cutting instructions. Or download 
CDR or DMG files for the laser cutter, or the print-scale PDF for hand cutting. 

• Use 3/16" balsa for fuselage and 1/16" balsa for wings. For best results, cut the horizontal 
stabilizer with the grain going lengthwise, and cut the vertical stabilizer (tail fin) with the 
grain going from top to bottom. 

• For hand cutting, the 3/16" balsa cuts well on a power scroll saw with a new blade. The 
bottom splinters a little, but can be sanded with fine sandpaper. I don't recommend cutting 
the 1/16" balsa with the scroll saw; instead, use a very sharp hobby knife, cut slowly with 
multiple passes, and use a metal straightedge when possible. 

• TIP: If you're hand cutting the fuselage, instead of cutting out the slot for the 
stabilizer, you can use a saw blade to cut inward from the rear of the fuselage. This 
is an easier cut, and as effective as the slot on the templates. 



* 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 2 




• Cut the wing pivot from 1/8" acrylic or hardboard, by hand or laser, using the 
corresponding downloaded file. Drill tiny holes with a 3/64" drill bit in the pivot in the exact 
location shown on the template. 

• TIPS: The wing pivot is a small piece, so use good-quality hardboard or the layers will 
come apart. 

• You can skip this next step if you are using the new plastic sleeve as described in the 
next step. This sleeve is provided in the new version of the kits. 

• Smooth the top and bottom edges of the pivot piece with sandpaper; otherwise the sharp 
square edges will tend to wear away at the balsa wood. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 3 




• If building from the kit, thanks to reader input, we have a NEW IMPROVED DESIGN 
feature! This thin plastic sleeve slips into the pivot hole for increased durability and 
reliability. 

• De-burr the plastic sleeve using your fingernail. 

• Push-fit the sleeve into the pivot hole on the fuselage. It should fit snug, but you could 
carefully put a couple drops of super glue along the seam between the sleeve and 
fuselage. Make sure you don't get glue inside the sleeve as you want the wing pivot to 
move smoothly. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 4 




• For the wing clips, use tinsnips to carefully cut the aluminum sheet into 2 pieces 7/8"x2 
1/2". If you're using a soda can, you can use scissors to cut and flatten it out, then cut it to 
the same dimensions. 

• Cut the 1/8" dowel to 1/2" for the wing stop, and the 1/4" dowel to 6" for the handheld 
catapult. For the rubber band tube, cut a 1/2" length of the rigid plastic tubing. A razor 
blade will make a clean cut. 



Step 5 — Make the wing clips. 






• To shape each wing clip, fold the aluminum piece in half lengthwise over a scrap of 5" 
balsa. A vise is helpful in starting the fold. Fold carefully so as to not split the aluminum on 
the fold. 

• Using a rotary tool, cut a notch about 1/8" wide and 3/16" deep into the folded side of the 
aluminum clip, 3/4" from one end, to accommodate the wing pivot. Debur the notch with a 
small file. 

• TIP: Mount your rotary tool in a vise for increased stability when cutting. 



it 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 6 




• To mount the wing clips, apply a tiny drop of Gorilla Glue to the top and bottom of the wing 
edge nearest the fuselage, and then slide the aluminum wing clip onto the wing end, 
leaving enough room for the wire rod to slide freely between clip and wing. 

• Once the glue dries, clear out the exposed balsa wood in the aluminum notch using the 
rotary tool. 

• Wing edges are fragile! Use great care when installing the wing clip so as not to 
break the wing edge. 

• Note on photo three how the straddle wire later fits into the wing clip. 

• TIP: Gorilla Glue works very well, but remember that it expands, so be sure to use 
only a tiny bit. - NEW DEVELOPMENT - use a couple tiny drops of super glue on 

the aluminum and wood seam. Dries fast and no expansion! 



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Step 7 — Assemble the fuselage. 



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• Cut the slot for the nose weight using a power scroll saw or coping saw. 

• Slip the penny into the nose slot and either glue the penny in place or dip the nose in 
PlastiDip. PlastiDip gives the nose a bit more durability for hard-surface landings, and 
looks nice as well. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 8 




• Use the rotary cutting wheel to cut a shallow groove in the top of the fuselage at the rear, 
sized to accept the tail fin. Depending on the thickness of the rudder (balsa tends to be 
inconsistent), you may need to widen the slot with a hobby knife. Be careful not to break 
the rudder in the process! 

• Insert vertical and horizontal stabilizer, make sure they're aligned, and then zap them with 
super glue. For additional strength, add a line of glue on all sides where the tail fin and 
stabilizer meet up with the fuselage. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 9 




• Glue the rubber band tube into the front hole in the top of the fuselage, spaced evenly on 
both sides. A tiny drop of Gorilla Glue adheres well to both plastic and wood. 

• Glue the wing stop (the 1/8" dowel) into the rear hole in the top of the fuselage with a tiny 
drop of Gorilla Glue as well. This piece will stop the wings' forward motion when they 
unfold. 

• You can skip this step if you are using the plastic sleeve (provided in new versions of the 
kit). See step 3. Otherwise, apply several layers of glue to pivot hole and launch slot to 
keep from wearing away the soft balsa. This will strengthen the balsa as this area tends to 
wear during use. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 10 — Mount the wings. 




• The straddle wire holds the 2 wings together and straddles the fuselage. Cut the wire to 
about 6 1/2". A large paper clip might work if you unkink it completely and bend it carefully. 

• Hold the wire in the center with needlenose pliers, and bend it over the pliers to create a U 
shape. Then hold the bent wire with pliers 7/8" from the top of the U and bend both legs 
upward at a 90° angle. 

• NOTE: This U-shaped saddle will straddle the fuselage and stop the wings' 
downward rotation into the horizontal position. The straddle wire can later be bent to 
adjust the angle of incidence in flight. 



it 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 11 










• Attaching the main wings to the fuselage using the straddle wire and wing pivot is the 
trickiest step and involves about 6 hands doing different things. Relax and be patient. 
You'll eventually get everything together correctly. 

• Before you begin, use a tiny piece of sandpaper and smooth the top and bottom 
edges of the small acrylic wing pivot piece. A smoother edge will help prevent 
the pivot from wearing away at the balsa in the pivot hole and move more smoothly. 

• Hold the wings in the folded-back position against the fuselage, slide in the pivot, and then 
insert the straddle wire down the gaps in the aluminum wing clips (between the wing and 
the clip), passing the wire through the holes in the pivot on both sides. 

• If one side of your wire is slightly longer, try to get that side into the pivot first. 

• The straddle wire can later be bent to adjust the angle of incidence in flight. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 12 — Attach the rubber band. 




• Turn glider over and stick staples through each wing behind the leading edge 1 3/4" from 
fuselage edge of the wing. It's critical that they are the same distance on each wing. 

• Flip the glider right side up and bend the staples over. Be sure not to tear the thin balsa 
wood. 



Step 13 




• Feed the small rubber band through the tube in the fuselage, then hook it onto the staples 
and bend them back firmly to secure it. 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 14 






• Loop the large rubber band around the end of the 1/4" dowel as shown. This is your 
handheld catapult. 

• The glider should unfold its wings in one quick motion. If the wing clips are rubbing the 
fuselage and preventing the wings from unfolding quickly, spread the straddle wire so that 
it pushes the wings slightly outward. 

• TIP: Loop the rubber band around the very tip of the dowel to minimize the chance 
of the glider hitting the dowel. 

• That's it! Now you're ready to get outside and launch your very own rocket glider. 



* 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 15 — Launch and soar. 




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• Safety precautions: To launch your glider, select a large ball field or open area 
away from trees. Grass is ideal, as landings on concrete or dirt tend to eventually 
eat away at the balsa wood. 

• As with any catapulted object, use caution when launching your glider. Always point the 
glider straight up. Never aim it at a person or thing. 

• Launch process: Flip the wings up, from horizontal to vertical. 

• Fold the wings back along the fuselage, so the wing tips are above the horizontal 
stabilizer. 

• Hook the catapult rubber band through the launch notch in the bottom of the fuselage. 

• Hold the catapult with one hand, and the folded wing tips with the other hand. Pull the 
glider back on the rubber band and launch it straight up! 



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Folding-Wing Glider: Rockets Up ... Glides Down! 



Step 16 — Launching tips 





• Try doing a glide test on soft grass to adjust your glider for a good glide before launching it 
high. To adjust the angle of incidence, carefully bend the straddle wire forward if the 
descent is a series of dips and stalls, or backward if the glide is too steep. 

■ It's very important to launch the glider straight up, so that it stalls and allows the 
wings to open. If it doesn't stall, it may just follow a curve and plow into the ground. 
Watch Video of Launch 

• The handheld launcher is ideal for ages 10 and up; you need longer arms to pull the glider 
back and get it up high. The higher you launch it, the better. This gives the wings plenty of 
time to unfold for a gentle glide down. 

• The glider is quite fragile, so caution kids running to retrieve it not to step on it in their 
enthusiasm! 

This project appeared in MAKE Volume 31 . page 88. 

This document was last generated on 201 3-02-1 9 10:1 2:52 AM. 



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